MONDAY, Feb. 7 (HealthDay News) -- If you suffer from allergies, take heart: Researchers say you may be less likely to develop a tough-to-treat brain cancer, possibly because your immune system is on high alert.

It's not clear how this knowledge might improve prevention or treatment of brain cancer, but the study's lead author said the findings pave the way for further research.

"We need to do more studies to really get at that underlying mechanism. Then we might be able to do things that would influence people who might have a higher risk or may have a family history," said Bridget J. McCarthy, a research associate professor of epidemiology at the University of Illinois at Chicago.

The lesions studied are known as gliomas, the most common type of adult brain tumor. They account for more than half of the 18,000-plus malignant brain tumors diagnosed in the United States every year, according to the U.S. National Cancer Institute.

Gliomas -- which led to the death of Sen. Edward Kennedy -- often cause death within months, despite surgery or treatment with chemotherapy or radiation.

Researchers have published conflicting studies about whether people with allergies and autoimmune disorders (which cause the immune system to attack the body) have a lower risk of developing the tumors, McCarthy said. "We wanted to look at the spectrum and see if we found the association with any type of allergy," McCarthy explained.

In the study, published Feb. 7 in the journal Cancer Epidemiology, Biomarkers & Prevention, McCarthy and colleagues examined surveys filled out by 419 patients with gliomas and 612 cancer-free patients from North Carolina and Illinois. All of the patients were asked if they had doctor-diagnosed allergies -- seasonal, medication, food, pet or any other -- and whether they took antihistamines.

The researchers found that patients with both high- and low-grade tumors were more likely to report no allergies than the other patients. And the more allergies someone had, the lower their odds of having gliomas. Antihistamine use didn't affect the results, the authors said.

However, the study didn't specify exactly how much more likely it is that an allergy-free person will develop a glioma compared to someone who has allergies.

What might allergies -- or the lack of them -- have to do with brain tumors? McCarthy said overactive immune systems may cause allergies and also allow people to fight off cancer. Figuring out what to do about this is the tough question.

"Obviously, it's not like allergies are a modifiable risk factor," she said. "You can't tell people to go out and develop allergies. That's not going to happen. And you can't tell people with allergies that, 'You're doing a good thing, and don't try to get rid of them.'"

The study doesn't prove a cause and effect -- that allergies directly lower the risk of brain tumor. It only shows a possible connection, one that doesn't sway Dr. Eugene S. Flamm, chairman of the department of neurosurgery at Montefiore Medical Center in New York City.

Flamm said the study is small and draws conclusions "far beyond the observational data."

"As the authors point out, there are several conflicting reports in the literature, and this paper does not resolve the issue in any way," Flamm said.

One reason for the conflicting reports, the authors said, was that "allergy" was defined differently in various studies -- sometimes broadly and sometimes narrowly, as in seasonal allergies alone. Further studies are essential, they said.

More information

For more about brain cancer, visit the U.S. National Library of Medicine.